The generation of water borne resins by free radical emulsion polymerization is generally carried out in the presence of a surface active agent (surfactant) which emulsifies the hydrophobic discontinuous phase in the aqueous continuous phase and imparts stability to the final polymer phase. The emulsion polymerization composition may be stabilized electrostatically by low molecular weight anionic, cationic, or non-ionic surface active agents, such as sodium dodecyl benzene sulfonate, or by "in-situ" surface active agents, generated from ionic free radical initiators. The emulsion polymerization composition may also be stabilized sterically by high molecular weight polymeric protective colloids such as polyvinyl alcohol. Surface active agents are integral ingredients in emulsion polymerization reactions which also include, but are not limited to, water, monomer, and a water-soluble free radical initiator. Monomers generally exhibit limited water solubility and surface active agents are required to emulsify water-insoluble monomers to facilitate the reaction between the monomer molecules and the water-soluble free radicals. The newly formed polymeric discontinuous phase must then be stabilized to coagulation by adsorption and/or grafting of a stabilizing species, which function is also generally carried out by the surface active agent.
While surface active or emulsifying properties may be common to emulsion polymerization and a variety of detergent, cosmetic, and industrial applications, it is not expected that a material found useful for one application will be suitable for emulsion polymerization. Conventional methods do not employ poly-amino acid derivatives as emulsifiers or stabilizers in aqueous free radical emulsion polymerization reactions. Many traditional emulsifiers and stabilizers have been disclosed for performing aqueous free radical emulsion polymerization but all have some limitations in terms of the processes and properties of the final product. The present invention provides an improved method for emulsifying and stabilizing an aqueous free radical emulsion polymerization reaction of ethylenically unsaturated monomers without many of the limitations characteristic of previously known methods.